Selective switching system for voltage regulation



SELECTIVE SWITCHING SYSTEM FOR VOLTAGE REGULATION Filed Aug. 3, 1953 llll llll llllll- INVENTORS JOZEF CORNELIS MOERKENS THEODORUS HEHENKAMP AGENT United States Patent 1 2,752,557 SELECTIVE SWITCHING SYSTEM FOR VOLTAGE REGULATION Jozef Cornelis Moerkens and Theodorus Hehenkamp,

Eindhoven, Netherlands, assign-ors to Hartford National Bani: and Trust Company, Hartford, Conn., as trustee Application August 3, 1953, Serial No. 372,310? Claims priority, application Netherlands August 29, 1952 Claims. (Cl. 32343.5)

The present invention relates to a selective switching system. More particularly, the invention relates to a system for selectively applying one of a plurality of predetermined different voltage sources to a given load.

In copending patent application Serial No. 364,746, filed June 29, 1953, there is described a system, more particularly for lighting airfields comprising a voltage divider which is adapted to be connected to a source of supply voltage and comprises a number of tappings for different voltages. Each tapping is adapted to be connected to the load via a separate switch and the switches are each operated by an electromagnetic relay. The energizing winding of each relay is adapted to be connected to a source of alternating voltage via a separate control switch. In this system, the common supply lead to the source of alternating voltage comprises the series-connection of a self-inductance and a capacitor which are so proportioned (for example such that the series-connection is in resonance at the frequency of the alternating supply-voltage) that if any of the control switches is in its operative position the voltage across the series-connection is so low that the remaining voltage across the connected relay-winding energizes the relay concerned. Each electromagnetic relay comprises an auxiliary contact which, in the energized condition of the relay, shortcircuits the capacitor, if desired through a resistor. The invention is based on the recognition that the impedance of an electromagnetic relay with its armature dropped away is much lower than that of the relay with its armature attracted. This permits the impedances to be so chosen that, after short-circuiting the capacitor, the selfinductance takes such a part of the operating voltage that the residual voltage on the energization winding of the energized relay (this winding has a high impedance, since the armature is being attracted) is sufliciently high to maintain the relay energized even if another control switch is closed. The voltage across the energization winding then connected which has a low impedance, since the armature is still dropped is insufficient to energize it, thus preventing part of the voltage divider from being short-circuited. Although the system described operates satisfactorily, it has a limitation in that, if another relay is to be connected, the relay previously connected must first be disengaged. The loss of time thus incurred may be disadvantageous, particularly in the case of airfield lighting.

This limitation is mitigated by the present invention.

According to the present invention the control switches in a system of the aforesaid type, when left to themselves occupy automatically the open position and each electromagnetic relay comprises a second auxiliary contact via which the relay is maintained energized after opening the control switch concerned. The impedances of the relays in closed condition are so high and in open condition so low that, if the control switch of another relay is closed and the second energization winding thereof is connected in parallel with the first-mentioned energized winding, the total impedance of the parallel-connected windings, and consequently the voltage across them, is so low relative to that across the self-inductance that the energized relay becomes de-energized, with the result that its energization winding is disconnected, the capacitor short-circuit is removed and the other relay is engaged.

This consequently permits the automatic changeover from one relay to the others practically without loss of time.

According to another feature of the invention, an auxiliary capacitor is connected in parallel with the energization windings of the relays and so proportioned that the impedance of said parallel-connection in the case of a relay with its armature attracted is high relative to the impedance of the aforesaid self-inductance.

In closed relays, this results in, due to the voltage being shared between the self-inductance and the parallel-circuit connected in series therewith, the voltage across the energization winding concerned rising to a considerable value, thus reducing the risk of de-energization of the relay due to supply source voltage fluctuations.

The impedance of the last-mentioned parallel-connection is preferably capacitative so that after short-circuiting the capacitor by the energized relay in the series-connection comprising the self-inductance, the voltage across said capacitative parallel-connection, hence across the relay winding, exceeds the supply source voltage, thus further diminishing the risk of de-energization of the relay in the case of supply voltage fluctuations.

According to a further feature of the invention, the system comprises means for remote control with long leads between the control switches to the relays. The self-inductance and the capacitor are so proportioned that the series-connection thereof at the frequency of the alternating voltage is capacitative such that this capacitative series-connection in series with the impedance of the relay winding with its armature attracted is at least substantially in resonance at the frequency of the alternating voltage. The decrease in current strength due to the ohmic resistance in the long leads is thus compensated to a greater or lesser degree. In the case of resonance the current strength is a maximum, hence the voltage across the relay winding also attains its maximum value and the armature is earlier attracted.

In order that the invention may be readily carried into effect it will now be described with reference to the accompanying drawing, given by way of example, in which the figure is a schematic diagram of a preferred embodiment of the present invention. In the figure, a source 1 of alternating voltage is connected to a transformer 2, whose secondary 3 comprises tappings 4, 5, 6 and consequently acts as a potentiometer. The tappings 4, 5, 6 may at will be connected via switches '7, 3, 9 to the load it), which may comprise, for example, an airfield lighting system.

The switches 7, 8, 9 are coupled to armatures 11, 12, 13 of electromagnetic relays 14, 15, 16, whose energization windings 17, 18, 19 are adapted to be connected via separate control switches 20, 21, 22 to a terminal of the source 1 of alternating voltage. The control switches are normally maintained open by springs.

The other ends of the energization windings 17, 18, 19 are connected through the series-connection of a selfinductance 23 and a capacitor 24 to the other terminal of the source 1 of alternating voltage. The relays comprise auxiliary contacts 25, 26, 27 short-circuiting the capacitor 24 in the energized condition of the relay concerned, for example the relay 14. The self-inductance 23 and the capacitor 24 are so proportioned that the series-connection of said two elements is to a greater or lesser degree in resonance with the frequency of the A. C. supply source 1.

Each relay further comprises auxiliary contacts 28, 29, 30 by means of which, after energization of the relay by closing any of the control switches, say 20, the relay is maintained energized, for example via the auxiliary contact 28.

Upon closing, for example, the control switch 20 the relay 14 becomes energized, while the energization wind- 'ice ing 17 on closing switch 20 is still supplied via the seriesconnection of the self-inductance 23 and capacitor 24. This is because prior to energization of the relay 14, i. c. with the armature 11 dropped, switch 25 is still open. Since the series-connection is in resonance to a greater or lesser degree, the energization winding 17 receives the full alternating voltage, apart from ohmic voltage losses in the series-connection, and the relay becomes energized. Due to this switch 7, the auxiliary contact 25 and the auxiliary contact 28 are closed, as shown in the drawing, the load being connected to the lowest voltage and the capacitor 24 being short-circuited. The control switch 20 may then be released and assumes automatically its open position.

By way of example it will be assumed that the impedance of each energization winding 17, 18, 19 is approximately 400 ohms with the armature dropped away and approximately 2500 ohms with the armature attracted. If the impedance of the self-inductance 23 is, for example, 700 ohms, the alternating voltage across the energization winding 17 after short-circuiting the capacitor 24 exceeds the full supply source voltage by approximately or more than If switch 21 is closed, the energization winding 18 is supplied with voltage through the self-inductance 23. Since the armature 12 is still dropped, the winding 18 has an impedance of 400 ohms. The total impedance of the parallel-connected windings 17 and 18 then amounts to approximately 345 ohms and the voltage across it or approximately one half of the initial value; hence the relay 14 becomes de-energized and the contacts 7, 25 and 28 are opened. Due to this the capacitor 24 is again connected in series with the self-inductance 23 and the relay 15 is automatically connected into circuit by the increased voltage. The source of voltage to which the potentiometer 3 is connected for the different voltages across the load 10 may alternatively be a source of direct voltage.

The impedance of the relay 15 with its armature attracted now amounts to 2500 ohms. Since a second capacitor 31 having a capacity of, for example, 0.7 microfarad, lies in parallel with the energization Winding 18, the oscillatory circuit thus formed may be in resonance at the frequency of the A. C. supply source; hence the impedance of this circuit becomes very high relative to the impedance of the self-inductance 23 of 700 ohms. This results in a much higher voltage being set up across the energization winding 18, and the risk of de-energization of the relay in the case of supply source voltage fluctuations is decreased considerably.

A still higher voltage may be set up across the energization winding 18 by making the impedance of said parallel-circuit sufiiciently capacitative so that in the seriesconnection comprising the self-inductance 23 the voltage across the parallel-circuit is higher than the supply source voltage.

In the case of remote control, the leads to the relays are very long, for example 1 /2 kilometers, with an airfield lighting system. These leads may have an ohmic resistance of approximately 80 to 100 ohms. In fact, the transformer 2 with the self-inductance 23, the capacitors .24, 31 and the relays 17, 18, 10 are situated in the proximity of the runways, whereas the control switches 20 to 22 are remote therefrom. With respect to switch 22 this is diagrammatically shown by long leads 32, shown in broken lines, and a switch 33 substituted for switch 22.

After the switch 33 has been closed to de-energize the relay 14, the series-connection of the self-inductance 23 and the capacitor 24 lies in series with the additional ohmic resistance of the long leads 32 so that the current strength through them is lower. In order to facilitate energization of the relay 16 the series-connection of 23 and 24 is capacitative to such a degree as to obtain at least substantially the case of resonance in series with the self-inductance of the relay winding 19 with open relay at the supply source frequency, so that the current strength becomes as high as possible and the voltage across the energization winding 19 is a maximum and may exceed the alternating supply voltage.

It is to be understood that the invention is not limited to the details disclosed but includes all such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A system for selectively applying one of a plurality of predetermined different voltage sources to a given load, said system comprising a plurality of switches, one of said switches being connected between each of said sources and said load, a plurality of electromagnetic relays, one of said relays being operatively coupled to each of said switches, an energizing source for said relays, a plurality of control switching means adapted to be normally in an open position, each of said relays having an energizing winding connected to one of said switching means, and a common lead including a series combination of an inductor and a capacitor connecting said relays via said switching means to said energizing voltage source, each of said electromagnetic relays having a first auxiliary contact and means connecting said auxiliary contact to short circuit said capacitor in the energized condition of the corresponding relay, said inductor and said capacitor having values at which a voltage from said energizing voltage source operates one of said relays when corresponding control switching means connect the energizing winding of said one relay to said energizing source, each of said relays having a second auxiliary contact via which the corresponding relay is maintained energized when only one of said control switching means connects one of said windings to said energizing source, the winding of each of said relays having an impedance value during its operating condition at which said one relay becomes de-energized when another of said switching means connects another of said relays in parallel with said one relay whereby the short circuit is removed from said capacitor and said another relay becomes energized.

2. A system as set forth in claim 1, further including an auxiliary capacitor connected in parallel with one of said relays when said one relay is in its operative condition, said auxiliary capacitor having an impedance value at which the impedance of the parallel combination of said auxiliary capacitor and said one relay in its operative condition is high relative to the impedance of said inductor.

3. A system as set forth in claim 2, wherein the impedance of the parallel combination of said auxiliary capacitor and said one relay is capacitative to provide a voltage across the parallel combination of said auxiliary capacitor and said one relay which exceeds the voltage of said energizing source.

4. A system as set forth in claim 3, wherein said control means includes long leads, said series inductor and capacitor having values at which said series combination is capacitative at the frequency of said energizing source to such a degree that said capacitative series combination in series with the impedance of said relay in its operative condition is substantially in resonance at the frequency of said energizing source.

5. A system as set forth in claim 4, wherein the im-.

pedances of said series inductor and capacitor have values at which the voltage across said one relay exceeds the voltage of said energizing source.

References Cited in the file of this patent UNITED STATES PATENTS 2,180,193 Brand Nov. 14, 1939 

